Telephone-receiver.



C. L. CHISHOLM.

TELEPHONE RECEIVER.

APPLICATION FILED mmm. 1910.

1,046,554, Patented Dec.10,1912.

CHARLES L. CHISHOLM, OF MARYSVILLE, NEW BRUNSWICK, CANADA, ASSIGNOR T CHISI-IOLM TRANSMITTER & TELEPHONE INSTRUMENTS GOMPANY.

TELEPHONE-RECEIVER.

Specification of Letters Patent,

Patented Dec.. MB, iwi?.

Application filed January 21, 1910. Serial No. 539,216.

To all whom 't may concern:

Be it known that I, CHARLES L. CHIS- HoLM, a citizen. ofl Canada, residing at Marysville, in the Province of New Brunswick', Dominion of Canada, have invented a new and useful Telephone-Receiver, of which the following is a specification.

This invention has reference to improvements in telephone receivers, though in part applicable to other acoustical instruments and its object is to provide means whereb;7 a diaphragm may be caused to respond with l greater accuracy than is the case with instruments of this character as ordinarily constructed.

In acoustical sound receiving instruments employing o r transmitting dia- 'f-phragms, such diaphragme are particularly strains susceptible to disturbing inliuences with consequent distortion of the sound waves with respect to the electrical undulations causing such sound waves through the intermediary of the diaphragm, or distortion of electrical undulations caused by the action of sound waves upon the diaphragm.

The ordinary diaphragm is circular and is supported at the periphery usually by means of two circular members in clamping relation, with the diaphragm edges between them. Even with the greatest care `in manufacture a diaphragm so mounted has disturbing zones of unequal strain or stress which interfere materially with the operation of the diaphragm either for receiving or causing soundwaves. Under commercial conditions the disturbing stresses and under which the diaphragme are placed become so marked as to interfere seriously with the propagation of overtones even to the obliteration of some of them and the timbre. of the sound, especially in the transmission of vocal'sounds is often sutliciently changed as to destroy the naturalness or .recognizability' of the voice.

By the present invention the ideal conditions for mounting of the diaphragm are .Closely approached and furthermore in the case of a telephone receiver these conditions :are not disturbed since the invention comprises means for establishing magnetic conditions co-acting with the diaphragm to cause a faithful response the diaphrag'rnI y to the electrical undulations entering the `re ceiver so that the resultant Waves caused by the diaphragm will not `be wanting in the delicate sound waves upon which thenaturalness or timbre of the sound depends.

The invention will.v bev best understood froma consideration of the following detail description taken in connection with theaccompanying drawings forming a part of this specification, in which drawings,

Figure 1 is a central longitudinal section of the hearing end of a telephone transmity ter with the invention applied thereto, the

showing being on la somewhat enlaigedv scale. Fig. `2 is perspective view ofthe pole pieces of the structure of F ig. l on a larger scale. Fig. 3 is an end view of the structure of Fig. 2, slightly modiied. Fig. 4 is a detail section of a portion of the da*u phragm and the support therefor on an en larged scale.

There is shown in Fig. l the ordinary casing 1 and cap 2 of an ordinary telephone receiver and these parts may be similar to vthe like parts of telephone receivers as com monly constructed. The cap 2 is provided with the usual cavity 3 for the reception of Y the ear of the user and this cavity `terminates at the inner. end in the usual sound passage 4:. Y I

l There is shown a diaphragm 5 which may consist of a circular iron disk such as is usually employed in connection with telephone receivers and other like instruments wherein a diaphragm is set in vibration by electrical impulses to cause the sound waves corresponding to such impulses, or Where the sound waves set the diaphragm into vi# bration to actuate Amembers which` in turn eol cause a record ofi-the sound Waves to be pro-I I duced or cause electrical undulations by means of which the sound may be transmitted to and reproduced at a distance. in the case of the transmission or recording of lthe sounds the diaphragm 5 need not of course be of magnetic material. The diaphragm is peripherally supported on a narrow ledge 6 formed in the inner Wall of laring 7. The ledge 6 is made as narrow as practicable so that a very much smaller area at the periphery ofthediaphragm/is engaged by the ledge thanv is the case in telephonereceiversmnd like acoustical instruments as ordinarily constructed. The diaphragm is lodged in the ring 7 under practically no stress or strain and is there secured by a suitable cement indicated at 8.

When the .parts are assembled the ring 7 with the diaphragm 5 cemented-thereto under practically no stress or strain, is seated on the usual ledge at the hearing end of the casing or hand hold land then the cap 2 is applied and screwed down on the ring 7 in-the same manner as this cap is usually screwed down upon the diaphragm, but the ring 7 is of suicient width and thickness to resist any action of the cap 2 to distort the ring from its original condi- 1 tion when the cap 2 is screwed against the ring in clamping relation thereto. The diaphragm 5 therefore remains in the originall condition under practically no stress or strain even when the ring 7a is clamped against the casing l by the cap 2 under conditions which would put a diaphragm directly clamped between these members under such distortion as to materially affect its action.y

By mounting the diaphragm in .a peripheral ring of such stiffness as to resist the distorting eiilects of clamping the ring in place, aclose approach to or the full attainment of the ideal condition may be had without danger of disturbing these conditions whenever it is necessary -to remove the clamp member and the diaphragm for inspection or repairs, the diaphragm, when`once set in the marginal ring maintaining its proper condition indefinitely and remaining unaffected by any stress or strain which might and does occur when the diaphragm is directly engaged bythe clamping surfaces;

The ring 7 may if desired be made of n some non-magnetic metal or of some other unyielding material, metal being usually preferred. For cementing the diaphragm to the ring 7 shellac has been found suitable, and this shellac may be either pure shellac or a mixture thereof with rosin. However theinvention is not at all limited to the particular kind of cement mentioned, but this cement should be of a firm, unyielding character. Under some circumstances metallic cement may be used. With a diaphragm so mounted there-is a succession of concentric zones from the center toward the periphery which will vibrate'in the order of the chromatic scale and these .Zones are without sensible distortion from stresses or strains due to the setting or clamping of the diaphragm.

With such a diaphragm as used'in a-telephone receiver experience has shown that the ordinary parallel pole pieces of the bipolar receiver are not so well adapted to cause the actuation of the diaphragm as are pole ypieces corresponding approximately to the shape of a zone of vibration of the diaphragm, especially when the zones are well marked as is the case with a diaphragm mounted as described herein. In accordance with the present invention there are provided separate pole pieces 9 of the Hat type commonly employed in bi-polar receivers, these pole pieces being surrounded by the usual coils 10, but at the outer or polar ends, the pole pieces are materially modified as best shown in Fig. 2. Projecting from the adjacent sides or `faces of the pole pieces immediately beyond the corresponding ends of the coils 10 are horns 114 at the outer corners of the pole pieces, these horns projecting one toward the other but with their terminal endsv nspacedapart so that while the horns of one pole piece project towardA the horns of the other pole piece they are separated by air gaps. The outer ends or polar extremities of, the pole pieces are of segmental contour and in the same plane, the outer corners of the horns where they merge into the bodies of the pole pieces being cut away as indicated at 12. In the structure shown in Fig. 2 the plane segmental pieces of the-polar extremities presented toward the diaphragm'have the inner and (guter edges concentric being all described about a common center and the continuity of 'these edges is broken only at the air gaps between the facing portions of the horns 1l, the plane faces of the polar extremities being of equal wid'thpthroughout and the curvature of the plane polar Jr'aces is such that ii. these faces were continued across the air 'gaps they would form a complete ring of equal width throughout. When the parts are assembled the center of curvature of the polar faces presented to the diaphragm should coincide as nearly as practicable with the center of the diaphragm so that the pull of themagnets on the diaphragm will be in a zone of one pitch. The

horns 11 are made to immediately overlie the corresponding ends of the coils 10 so that the polar extensions are of the shortest practicable projection. The air gaps between thel horns 11 are so proportioned to the distance between the plane polar -faces of the pole pieces and the adjacent face of the diaphragn thatlleakage across these air gapsis reduced to a minimum and consequently the full pullof the magnet pole pieces is exerted von the diaphragm and this pull is concentric with the center of the diaphragm in a zone of one pitch. Practical experience has shown that distortion or disturbance of the diaphragm is thus avoided and marked purity of tone results. lSince there-may be a tendency of magnetic leakage across the air ga with a consequent disturbance of the uniformity of the distribution of magnetism in the polar extremities, the ends of the horns of each pole piece where facing the corresponding ends of the horns of the other pole piece may be reduced as indicated in Fig. 3, or maybe otherwise modified so that the magnetic leakage iscorrespondingly reduced.

What is claimed is 1. In an acoustical instrument, a diaphragm having a stiff, unyielding peripheral setting individual to the diaphravm and to which the latter is firmly secured without stress or strain, the seat for the diaphragm in its setting being of inconsiderable radial extent.

2. In an acoustical instrument, a diaphragm, and a ring individual to the diaphragm and resistant to distorting forces and to which the diaphragm is firmly se cured without stress or strain.

3. In an acoustical instrument, a diaphragm, and a stili unyielding ring united to the periphery of the diaphragm Without stress or strain, the diaphragm and its peripheral ring being bodily attachable to and movable from the acoustical instrument in which it is used.

4. A telephone receiver having a dia phragm with a peripheral setting resistant to distorting forces individual thereto and provided with a' seat of inconsiderable radial extent for the diaphragm,and means for holding the diaphragm to its seat Without stress or strain.

A telephone receiver having an electromagnet provided with straight pole pieces each terminating ina polar face in line with the body portion of the pole piece and provided with laterally curved portions at the polar ends, the curved portions of one pole piece being directed toward tllose of the other and concentric with the longitudinal central axis of the magnet, thoseextremities of the straight portions and ot the curved portions together constituting the polar faces of the pole pieces being all in one plane.

6. In an acoustical instrument, a diaphragm free from stress and strain and provided with a peripheral portion individual thereto and resistant to forces tending to impart stress or strain to the diaphragm incident to clamping -said peripheral p0rtion in an acoustical instrument.

7. In an acoustical instrument, a diaphragm and a ring individual to the diaphragm and resistant to distorting forces and to which the diaphragm is firmly cemented substantially' without stress or strain.

8. In an acoustical instrument, a ring of stit, unyielding material having a seat of -inconsiderable radial extent in its inner edge, and a. diaphragm. firmly cemented to said seat substantially 4Without stress or strain.

9. In an acoustical instrument, a diaphragm having a stiff unyielding peripheral setting individual to the diaphragm and provided with a seat for the diaphragm of inconsiderable radial extent, and a firm cement uniting the diaphragm peripherally to the setting substantially with'outstress or strain.-

10. A telephone receiver having a d1a phragm with a peripheral setting lndivldual thereto and provided with a seat of 1nconsiderable radial extent for the diaphragm, and a cement for holdin the diaphragm to its seat Wlereby the diaphragm is substantially free from stress or strain.

In testimony that I claim the foregoing) as my own, I'liave hereto affixed my signay ture in the presence of two Witnesses.

CHARLES L. CIIISHOLM. Witnesses ROLAND C. BOOTH, C. E. DoYLE. 

